Sound Wave Oscilloscope

Teaching sound physics and related topics presents an excellent opportunity to have students build a simple oscilloscope to examine and study the nature of sound waves.

Items

You can make the oscilloscope using a can, a balloon, a small mirror and an inexpensive laser level. If you don’t have a ring stand, you can improvise one using wooden dowels inserted into pre-drilled holes in scrap lumber serve. Glue a small piece of mirror onto a balloon that is stretched over a metal cylinder made from a coffee can. Aim the laser at the mirror and direct the reflected laser beam onto a wall (as far away as possible as this will enlarge the pattern of vibrations that is observed and make for a more striking experiment).

When speaking into the can, the sound waves cause the membrane (and the mirror attached) to vibrate. The laser beam reflecting off the mirror also oscillates, allowing students to see a pattern of these vibrations on the wall.

If you are able to use a large darkened space, such as an auditorium or gymnasium, you may be able to produce a very large “web” of sound waves on a far wall. You may also “test” various sounds by inviting students to sing or play an instrument note into the can. Use a tuning fork to demonstrate visually the distinction between a pure tone and a combination of tones, such as the sound of the human voice.
Also try your oscilloscope with infrasonic and ultrasonic sound waves by using dog whistles, cell phone tones or swinging a pool hose slowly, then quickly. For fun, place one in front of the speaker at a school dance for an inexpensive “light” show as the beam oscillates on the ceiling.